Carbon combustion furnace



March 1933- c. B. FRANCIS CARBON COM4BUSTION FURNACE Filed July 14, 1931 2 Sheets-Sheet l jnvenior:

xm kuw March 28, 1933. c. B. FRANCIS CARBON COMBUSTION FURNACE Filed July 14, 1931 2 Sheets-Sheet 2 Patented Mar. 28, 1933 UNITED STA CHARLES 3. was; or PITTSBURGH, PENNSYLVANIA CARBON COMBUSTION FURNACE Application filed July-14,

This invention relates to electrically heated laboratory combustion furnaces and, while not limited thereto, relates more specifically to furnaces of this type adapted to determine the carbon in iron and steel by direct combustion of the metal, and has" for one of its objects the provision of a furnace adapted to maintain a temperature of more than 1000 degrees centigrade.

A further object is to provide a furnace of this type which is especially adapted for using rigid rod resistors.

Another object is to generally improve furnaces of this type, making them more adaptable to high temperature physical and chemical tests and giving conditions whereby more accurate'an'd complete determinations of carbon may be made than with furnaces of the prior art.

In the drawings:

Figure 1 is a sectional plan showing a furnace constructed in accordance with my invention.

Figure 2 is an end elevation partly in section.

Figures 3 to 5 are circuit diagrams showing various Ways of connecting the resistors.

Referring more particularly to the drawings, the numeral 2 designates the tubular body of the furnace which is composed of a high refractory material. End Wall members 3 of high refractory material are mounted at each end of the body 2 and the whole is enclosed in a metal casing 4. The interior surface of the tubular body 2 is lined with a special refractory material 5 capable of reflecting light and heat at high temperatures.

The end walls 3 are provided with centrally arranged apertures 6 to permit the mounting of a combustiontube 7' axially through the furnace with its ends projecting beyond each end wall 3.

A plurality of other diametrically opp osite openings or apertures 8 are formed in the end walls 3 spaced equally from each other and from the central aperture 6.

The apertures 8 flare outwardly and are conical in shape and have their inner or small ends surrounded by a wall portion 9 1931. Serial No. 550,773.

composed of a refractory characterized by being a good conductor of heat and a nonconductor of electricity.

Resistor elements 10 in the form'of rigid bars are mounted in the heating chamber of the furnace with their ends projecting outwardly into the conical openings 8. The resistors are adapted to generate sufiicient heat to maintain a temperature above 1000 degrees centigrade and not to oxidize or disintegrate at any temperature up to 1500 degrees centlgrade. The portions 9 of the Walls surrounding the small ends of the openings 8 fit closely the ends of but do not make act'ual contact with the resistors 10 and, due to the heat conductlng qualities of said walls, they help to prevent the resistors from developing hot spots at their points of contact with the metal lugs 17.

The conical shape of the openings 8 permits atmospheric air to circulate around the terminal ends of the resistors to prevent overheating of said ends. v I v Each end wall is provided with integral protuberances or lugs 14 made of heat resistant electrical insulating material ad'acent each of the'openings 8, and spring me al contact bars 15 are secured to said lugs by binding posts 16. Contact lugs 17 are carried by the ends of the bars 15 and engage the ends of the electrodes.

' In operation, the electric current is permitted to flow through the resistors 10 until the furnace temperature is raised sufliciently high when the material to be tested is placed in the tube 7 and, if desired, treated chemically by passing gases through the tube 7- v w The resistors may be connected in parallel, invseries parallel, or in series according to the voltage of the electric current being used, or to change the amount of heat produced.

'95 1 In Figure 3 theresistors 10 are shown diagrammatically connected in parallel.

In-Fig. 4 the resistors 10 are shown dia grammatically connected in series pairs with the pairs in parallel.

1 end walls,

In Figure 5 the resistors 10 are shown diarammatically connected in series.

Suitable safety shields 19 are secured to the end walls 3 of the furnace and are preferably formed of insulating material so as to guard against the operators coming into engagement with the contacts or other furnace parts.

While I have shown and described one specific form of my invention it will be understood that I do not thereto since various modifications may be made without departing from the scope thereof, as defined in the appended claims.

I claim:

1. A laboratory carbon combustion furnace comprising a hollow body portion and end walls, said body and end walls being composed of a highly refractory material and forming a heating chamber, said end walls being provided with centrally arranged openings to receive the ends of a combustion tube, a combustion tube mounted in said furnace axially of said chamber and with its ends projecting through and snugly fitting said openings, said end walls being provided with a plurality of other openings at diametrically opposite points around and spaced from said tube, rigid one-piece bar-type resistors extending through said furnace parallel to said tube and projecting through said last named openings, and means for forming an electrical connection with the ends of said resistors.

2. A laboratory carbon combustion furnace comprising a hollow body portion and said body and end walls being composed of a highly refractory material and forming a heating chamber, said end walls being provided with centrally arranged openings to receive the ends of a combustion tube, a combustion tube mounted in said furnace axially of said chamber and with its ends projecting through and snugly fitting said openings, said end walls being provided with a plurality of other openings at diametrically opposite points, around and spaced from said tube, rigid one-piece bar-type resistors extending through said furnace parallel to said tube and projecting through said last named openings, spring pressed contact members carried by the end walls of said furnace and engaging the ends of said resistors, and binding posts for permitting electrical connections with said contact members.

3. A laboratory carbon combustion furnace comprising a hollow body portion and end walls, said body and end walls being composed of a highly refractory material and forming a heating chamber, said end walls being provided with centrally arranged openings to receive the ends of a combustion tube, a combustion tube mounted in said furnace axially of said chamber and with its ends projecting wish to be limited.

through and'snugly fitting said openings, said end walls being provided with a plurality of other openings at diametrically opposite points around and spaced from said tube, said openings having at least a portion of their surrounding walls composed of a highly refractory material characterized by being a good conductor of heat and a nonconductor of electricity, rigid one-piece bartype resistors extending through said furnace parallel to said tube and projecting through said last named openings, and means for forming an electrical connection with the ends of said resistors,

4. A laboratory carbon combustion furnace comprising a hollow body portion and end walls, said body and end walls being composed of a highly refractory material and forming a heating chamber, said end walls being provided with centrally arranged openings to receive the ends of a combustion tube, a combustion tube mounted in said furnace axially of said chamber and with is ends projecting through and snugly fitting said openings, said end Walls plurality of other openings at diametrically opposite points around and spaced from said tube, said openings being of outwardly flaring conical shape and having their inner small end portions of their surrounding walls composed of a highly refractory material characterized by being of a good conductor of heat and a non-conductor of electricity, rigid one-piece bar type resistors extending through said furnace parallel to said tube and projecting through said last named openings so that their ends terminate in said openings, and means for forming an electrical connection with the ends of said resistors.

5. A laboratory carbon combustion furnace comprising a hollow body portion and end walls, said body and end walls being composed of a highly refractory material and forming a heating chamber, said end walls being provided with centrally arranged openings to receive the ends of a combustion tube, a combustion tube mounted in said furnace axially of said chamber and with its ends projecting through and snugly fitting said openings, said end walls being provided with a plurality of other openings at diametrically opposite points around and spaced from said tube, said openings being of outwardly flaring conical shape and having their inner small end portions of their surrounding walls composed of a highly refractory material characterized by being a good conductor of heat and a non-conductor of elec tricity, rigid one-piece bar-type resistors extending through said furnace parallel to said tube and projecting through said last named openings so that their ends terminate in said openings, spring pressed contact members carried by the end walls of said furnace and engaging the ends of said resistors, and bindill ing posts for permitting electrical connections with said contact members.

6. A laboratory carbon combustion furnace comprising a hollow body portion and end walls, said body and end walls being composed of a highly refractory material and forming a heating chamber, said end walls being provided with centrally arranged openings to receive the ends of a combustion tube, a combustion tube mounted in said furnace axially of said chamber and with its ends projecting through and snugly fitting said opening, said end walls being provided with a plurality of other openings at diametrically opposite points around and spaced from said tube, said openings being of outwardly flaring conical shape and having their inner small end portions of their surrounding walls composed of a highly refractory material characterized by being a good conductor of heat and a non-conductor of electricity, rigid' one-piece bar-type resistors extending through said furnace parallel to said tube and projecting through said last named openings so that their ends terminate in said openings, spring pressed contact members carried by the end walls of said furnace and engaging the ends of said resistors, and an insulating shields enclosing each end of said furnace to prevent accidental engagement with said contacts. 1

7. A laboratory carbon combustion furnace comprising a hollow body portion and end walls, said body and end walls bein composed of a high refractory material an forming a heating chamber, said end walls being provided with centrally arranged openings to receive the ends of a combustion tube, a combustion tube mounted in said furnace axially of said chamber and with its ends projecting through and snugly fitting said openings, rigid bar type resistors extending through said furnace parallel to said tube and arranged around and spaced from said tube, and means for forming an electrical con- =nection with the ends 3f said resistors.

8. A laboratory carbon combustion furnace comprising a hollow body portion and end walls, said body and end walls being composed of a high refractory material and forming a heating chamber, said end walls being provided with centrally arranged openings to receive the ends of a combustion tube, a combustion tube mounted in said furnace axially of said chamber and with its ends projecting through and snugly'fitting said openings, rigid bar type resistors extending through said furnace parallel to said tube and arranged around and spaced from said tube,

and means outside of said end walls for forming an electrical connection with the ends of said resistors.

9. A furnace comprising a heatin chamber, heating elements therein, a mu e endsupport in walls of said chamber and havmy hand.

CHARLES B. FRANCIS. 

